No trailing slash on root dir breaks posts_nav_link

Description

I've never submitted a bug so bear with me - I did a search prior to submitting and couldn't find this...

Found this in wpmu but the source came from wp - we had a problem where if you visit one of our blogs without the trailing slash - (blogs.example.com/subblog) the the paging features of posts_nav_link would produce funky links like blogs.example.com/subblog/subblog/page/2/ (notice the doubled 'subblog')

Some digging led to:

In link-template.php find (wpmu 1.2.1 - not sure about other versions or wp):

sets the value of $qstr to the same thing regardless of whether the path in the browser ends with a slash or not.
The old way (with 'trailingslashit') would try to match home_root (blogs.example.com/subblog/) against the path in the browser (blogs.example.com/subblog) which doesn't match.

I've hit this problem as well in the latest version of WPMU. This isn't the same issue as #1341. The problem is completely solved by removing the "$home_root = trailingslashit($home_root);" line like originally stated in the bug. Please investigate and fix this in the WP source code so I don't have to re-enter this fix into our code base each time we update WPMU. Please let me know if you need help seeing this issue. Thanks!